Abstract
South American fire ant decapitating flies in the genus Pseudacteon (Diptera: Phoridae) are potential biocontrol agents of the invasive fire ants Solenopsis invicta and S. richteri in the United States and other regions of the world due to their high host specificity and the direct and indirect damage to their host ants. Despite their importance and the fact that several flies have already been released in the US, little is known about the genetic variability and phylogenetic relationships of Pseudacteon flies parasitizing South American fire ants in the Solenopsis saevissima species-group. A species delimitation analysis was conducted using a distance-based method (ABGD) and two tree-based methods (GMYC and mPTP) using COI sequences of 103 specimens belonging to 20 of the 22 Pseudacteon species known from southern South America. Additionally, phylogenetic relationships between the already described and new candidate species were inferred using mitochondrial (COI) and nuclear (wingless) sequences. The species delimitation analysis suggests that species richness in these flies has been previously underestimated, due to the existence of putative cryptic species within nominal Pseudacteon obtusus, P. pradei, P. tricuspis, P. cultellatus, and P. nudicornis. Geographic distribution and host fire ant species seem to support cryptic lineages, though additional morphological data are needed to corroborate these results. All phylogenetic analyses reveal that South American fire ant decapitating flies are grouped into two main clades, with Pseudacteon convexicauda sister and well differentiated relative to these clades. Neither host nor geographic association appeared to be related to the differentiation of these two main clades within South American fire ant decapitating flies. This work provides information that will allow testing whether the putative cryptic phorid fly species show differences in their effectiveness as biocontrol agents against the highly invasive imported fire ants.
Highlights
Fire ant decapitating flies belong to the genus Pseudacteon Coquillett 1907 (Diptera: Phoridae) and derive their common name from their parasitoid life cycle in which their host ants are decapitated after the fly finishes its development inside the ant’s body [1, 2]
Most previous studies on South American fire ant decapitating flies have been focused on understanding their host specificity [10, 53, 54], behavior and activity patterns [1, 23, 55], or geographical distribution [22, 25, 56]
We found that the 20 Pseudacteon species studied in this work that parasitize fire ants of the S. saevissima species-group belong to at least 24 to 27 species
Summary
Fire ant decapitating flies belong to the genus Pseudacteon Coquillett 1907 (Diptera: Phoridae) and derive their common name from their parasitoid life cycle in which their host ants are decapitated after the fly finishes its development inside the ant’s body [1, 2]. The only possible host switch was reported for Pseudacteon fowleri Pesquero 2000, which is known to parasitize S. saevissima species-group, but was collected in the range of S. geminata species-group (in French Guiana and Guyana) [11]. These specimens were captured in malaise traps and their host is uncertain, they were placed as part of the ornate oviscapes group defined by [11] due to their morphologically similar genitalia. It is possible that the existence of cryptic species underlies this apparent host switch [11]
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